The usual intent in this art is to ensure disengagement or release of the projectile's driving groove faces without exerting unbalanced forces on the projectile, to avoid disturbing its flight. Symmetric construction and application of aeroballistic, muzzle blast, and/or inertial forces have been the primary means of controlling the discard. A form of bore-riding metal band at the forward end of the sabot, with weakening notches at the sabot petal interfaces, is applied in service armor-piercing, discarding sabot long rod penetrator ammunition. At shot ejection, the muzzle blast acts on a rear scoop on the saddle-type sabot petals. Each petal hinges open around a line through each pair of weakened portions of the band, lifting cleanly away from the driving lands. After a short opening rotation of the petals, from the rear, the material in the weakened portion breaks, releasing the separate petals to act individually. The aerodynamic forces on the front scoop then cause the forward end of the petals to rotate away from the long rod projectile, or penetrator, effecting full separation.
In another long rod penetrator sabot design, a small metal ring called a tipping ring is attached to the rear of the ramp sabot to keep the ends down against the stripping action of the muzzle blast, until aerodynamic forces on the forward scoops rotate the front of the sabot petals well away from the projectile body.
There are a number of issues associated with each of these approaches. In the latter round, the tipping ring fails to remove the sabot from contact with projectile promptly as the sabot begins to rotate open. With the discard trajectory of the sabot petals otherwise unconstrained, the forces opening the sabot and the long lever arm over which they operate can result in the tearing out of a number of the small driving lands on the rear portion of the sabot. Exertion of these unsymmetric forces on the projectile can cause significant round-to-round dispersion. The metal band on the former round is quite effective, but by its placement it limits the trajectories available. Furthermore, because it combines the functions of hinge and bore rider, the selection of materials from which it can be made is limited. Though a relatively small part of the total in-bore mass, it is nonetheless a parasitic mass. Location at the outer end of the sabot maximizes that mass for a given cross-section, as does the requirement that it be made of metal rather than polymeric plastic material or other light weight materials. Furthermore, the placement of the band at the periphery of the sabot results in the center of pressure of the muzzle blast lying inside the line of action of the hinge sections unless the saboted round is close to half bore diameter. This is not the case with present long rod penetrator ammunition. When the center of pressure of the muzzle blast is inside the axis of the hinges, the petals' form drag tends to keep them closed. The much lower force of lift coupled with blast infiltration must be utilized to effect their opening.